Endobacteria (Firmicutes)

The Firmicutes (Latin: firmus, strong, and cutis, skin, referring to the cell wall) are a division of bacteria, most of which have Gram-positive cell wall structure. A few, the Mollicutes or mycoplasmas, lack cell walls altogether and so do not respond to Gram staining, but still lack the second membrane found in other Gram-negative forms. Others, such as Megasphaera, Pectinatus, Selenomonas, and Zymophilus, have a porous pseudo-outer-membrane that causes them to stain Gram-negative. Scientists once classified the Firmicutes to include all Gram-positive bacteria, but have recently defined them to be of a core group of related forms called the low-G+C group, in contrast to the Actinobacteria. They have round cells, called cocci (singular coccus), or rod-shaped forms.

Many Firmicutes produce endospores, which are resistant to desiccation and can survive extreme conditions. They are found in various environments, and the group includes some notable pathogens. Those in one family, the heliobacteria, produce energy through photosynthesis. Firmicutes play an important role in beer, wine, and cider spoilage.

Health Implications
The division Firmicutes as part of the gut flora has been shown to be involved in energy resorption and obesity.

Laboratory Detection
While there has up to this point in time not been a way to categorically define a given bacterium as belonging to Firmicutes, as the phylum is highly diverse in phenotypic characteristics due to promiscuous plasmid exchange across species and genera of this phyla, the presence of Firmicutes can now be detected by real-time PCR using the methodologies recently described.